Apparatus and process for measuring the light transmission of a pigmented paint film

ABSTRACT

The apparatus is used for measuring the light transmission of a pigmented paint film and comprises A HOUSING HAVING POSITIONED THEREIN A MICROAMMETER ELECTRICALLY ATTACHED TO A PHOTOELECTRIC CELL AND TO A POTENTIOMETER WHICH IS USED TO ADJUST THE MICROAMMETER; AN INCANDESCENT LAMP POSITIONED INSIDE THE HOUSING AND A BEAM OF LIGHT FROM THE LAMP IS DIRECTED THROUGH AN OPENING IN THE HOUSING ONTO THE PHOTOELECTRIC CELL; A PIGMENTED PAINT FILM IS PASSED BETWEEN THE PHOTOELECTRIC CELL AND THE BEAM OF LIGHT FROM THE LAMP THEREBY CHANGING THE AMMETER READING; THE AMOUNT OF PIGMENTATION IN THE PAINT FILM AND THE THICKNESS OF THE FILM ARE DIRECTLY RELATED TO THE AMMETER READING; AN IMPROVED PROCESS FOR PREPARING PIGMENTED PAINTS USING THE ABOVE APPARATUS IS ALSO A PART OF THE INVENTION.

ilnited States Patent [1 1 Kornodromos Sept. 3, 1974 APPARATUS AND PROCESS FOR MEASURING THE LIGHT TRANSMISSION OF A PIGMENTED PAINT FILM [75] Inventor: Nicos M. Komodromos, Flint, Mich.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

22 Filed: Dec. 26, 1972 21 Appl. No.: 318,501

[51] Int. Cl. G01m 21/06, G0lj 3/46 [58] Field of Search 356/201-206, 356/218; 250/218, 573, 574

[56] References Cited UNITED STATES PATENTS 2,406,716 8/1946 Sweet 356/202 2,834,247 5/1958 Pickels 3,614,241 10/1971 Sanford et al. 356/203 OTHER PUBLICATIONS Mitton, Paint Testing Manual (Chapter 1-3), Thirteenth Ed., 1972, pp. 22-25 & pp. 38-39. Bruehlman et al., J. of Paint Technology, Vol. 41, No. 538, November, 1969, pp. 584-596.

' potentiometer Primary ExaminerRonald L. Wibert Assistant ExaminerR. J. Webster [5 7 ABSTRACT The apparatus is used for measuring the light transmission of a pigmented paint film and comprises a housing having positioned therein a microammeter electrically attached to a photoelectric cell and to a which is used to adjust the microammeter;

an incandescent lamp positioned inside the housing and a beam of light from the lamp is directed through an opening in the housing onto the photoelectric cell;

a pigmented paint film is passed between the photoelectric cell and the beam of light from the lamp thereby changing the ammeter reading;

the amount of pigmentation in the paint film and the thickness of the film are directly related to the ammeter reading;

an improved process for preparing pigmented paints using the above apparatus is also a part of the invention.

2 Claims, 3 Drawing Figures PATENIEDSEP 312133.306

m 1 W Z FIGJ PAIENIEU 3.833.306

sum ear 2 F l G. 2

SUPPLY NC 0 vous n lo APPARATUS AND PROCESS FOR MEASURING THE LIGHT TRANSMISSION OF A PIGMENTED PAINT FILM BACKGROUND OF THE INVENTION This invention relates to an apparatus for measuring the light transmission of pigmented films and an improved process for preparing the pigmented paints.

The determination of the necessary level of pigment in a paint film to give the desired amount of hiding with a certain thickness of paint film has been a subjective method. A standard was established in which a paint film at a given thickness should completely hide a black and white checked background or any other contrasting background such as a gray-black checked background. In a paint manufacturing process after the pigment was added, a paint film was sprayed onto a standard panel having a black and white checked background until the background was covered by the paint film and then the paint was subsequently dried. If the film was thicker than the established standard film, more pigment was added to the paint or if the film was thinner than the standard, additional unpigmented vehicle was added to the paint. However, this method was subjective and depended on the operator who visually determined the level at which the paint film hid the background and often variation from batch to batch and particularly from manufacturing plant to manufacturing plant occurred.

There is a need to accurately determine the pigment level in a paint by an instrument to achieve uniform results. Unnecessary pigmentation of a paint increases the cost and also changes the physical properties of the paint while insufficient pigmentation increases application costs since more paint is required to achieve the same level of hiding as a correctly pigmented paint. The movel apparatus and procedure of this invention provides a method for accurately determining the pigment level of the paint.

SUMMARY OF THE INVENTION The apparatus of this invention measures the light transmittance of a pigmented film and comprises a housing;

a microammeter having a dial for indicating electrical current firmly positioned in the housing and electrically connected to a potentiometer and a photoelectric cell;

a plate having a recess on one side thereof firmly attached to the housing wherein a recess in the plate and the housing define a slot;

a photoelectric cell electrically connected to the microammeter and positioned between the recess of the plate and the housing and firmly attached to the plate providing sufficient space between the photoelectric cell and the housing so that a pigmented paint film can be passed through the slot and between the photoelectric cell and the housing;

a potentiometer is attached to the housing and electrically connected to the photoelectric cell providing a means to adjust the reading of the microammeter;

an incandescent lamp is positioned inside the housing and connected to an electric power source;

the housing defines an opening positioned so that a beam of light from the incandescent lamp is directed onto the photoelectric cell;

wherein the light transmittance of the pigmented paint film is measured by adjusting the microammeter to a standard value with the potentiometer and by passing the film through the slot between the photoelectric cell and the housing interrupting the beam of light from the incandescent lamp which causes a change in the microammeter readthe microammeter reading is directly related to the level of pigmentation in the paint film at a given film thickness;

a process for measuring the light transmission of a pigmented paint film and an improved process for determining the level of pigmentation in paints to provide a uniform level of hiding power is also part of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a drawing of the apparatus of this invention.

FIG. 2 shows the electrical circuit for the incandescent lamp.

FIG. 3 shows the electrical circuit for the photoelectric cell, the microammeter and potentiometer.

DETAILED DESCRIPTION OF THE INVENTION The apparatus of this invention is shown in FIG. 1. The housing 1 can be made of metal or plastic and holds the components of the novel apparatus. An ammeter is positioned in the housing 1 and attached thereto. The frame 2 holds the dial assembly 8 of the ammeter, which is numbered and amperage is indicated by the indicator needle 9. Since the current readings are very small, a microammeter is used in the apparatus.

Attached to the housing I is a metal plate 3 having a recessed portion 5, and attached to the plate is a photoelectric cell 4. Sufficient space is left between the recess area of the plate 3 and the housing and the photoelectric cell 4 to permit a paint film to be passed through this area.

The photoelectric cell 4 is electrically coupled to the microammeter so that a .change in the light intensity will be indicated on the ammeter. FIG. 3 shows the electrical connection of the photoelectric cell 4 to the microammeter l4 and the potentiometer 11. The potentiometer dial 6 positioned on the housing is used to adjust the potentiometer. Optionally, a switch 15 can be used to break the circuit and turn off the microammeter and is normally attached to the housing as shown in FIG. 1.

Positioned in the housing 1 is an incandescent lamp 10 that is attached to an electrical receptacle 16 which is electrically attached to a power source. A beam of light from the incandescent lamp shines through a hole 7 defined by the housing and onto the photoelectric cell 4. Any change in the light intensity is measured by the microammeter 14.

. FIG. 2 shows the circuit where in the incandescent lamp I0 is attached in parallel to an indicator light 17. The indicator light shows whether or not the instrument is on. A 1 l0 volt of electricity is supplied through a conventional power plug 13 (FIG. 1). Optionally, a switch 12 can be used to turn off the apparatus and is mounted next to the switch 15 for the microammeter.

The potentiometer 11 is used to adjust the microammeter reading and standardize the apparatus. In the operation of the novel apparatus, a standard of a pigmented plastic sheet having a known reading on the microammeter is positioned in the slot between the photoelectric cell 4 and the beam of light from the incandescent lamp 10. The potentiometer 11 is adjusted by the dial 6 so that the microammeter reading will be the same as the established standard value. A potentiometer having a rating of 250 amps and 2,500 ohms can be used in the novel apparatus.

In the operation of the novel apparatus, a pigmented paint film is passed through the slot between the photoelectric cell 4 and the housing 1 and through the beam from the incandescent light 10 which causes a change in the light intensity. This change is registered by the microammeter. The thickness of the pigmented paint film is then measured by a standard gauge such as a Federal Gauge or a micrometer caliber. A relationship between the pigment content of the paint film, the thickness of the paint film and the microammeter reading is established.

One practical means for using this apparatus is to prepare a standard pigmented paint. This paint is sprayed over a transparent heat resistant flexible sheet placed over a black and white checked surface and sufficient paint is sprayed so that the background is rendered invisible to the unaided eye. The coated flexible sheet is allowed to dry either by baking if the paint is an enamel or lacquer or if other paints, by air drying. Then the microammeter reading of this paint film is determined by the novel apparatus and the thickness of the paint film is measured. This provides a standard to which all other paint samples are then matched.

In a paint manufacturing process to check the pigmentation of the paint, a paint film is sprayed onto a polyester substrate and then baked for minutes at about 110C. The paint is applied to insure complete black and white hiding at one end of the polyester substrate but at the opposite end of the substrate, the paint is sprayed so that incomplete black and white hiding is achieved. The novel apparatus is then standardized as shown above and the coated film is then passed through the slot of the apparatus of this invention under the photoelectric cell. As the paint coated substrate is passed through the slot in the apparatus, the reading on the microammeter is noted and when the reading on the microammeter is equal to the reading of the standard sample, the film is marked and the paint thickness is measured. If the paint film thickness is greater than the standard, additional pigment is added to the paint and the above test procedure is repeated. If the paint film thickness is less than the standard film, then additional unpigmented vehicle is added to the paint and the test procedure is repeated. This is repeated until the correct level of pigmentation in the paint is achieved.

The novel apparatus of this invention provides a means of accurately measuring the pigment level in a paint. Visual operator determination of the pigment level by determining hiding is eliminated along with the human errors of this subjective test. It is now possible to prepare paints with the same pigmentation level and provide for uniform paints from batch to batch and from one manufacturing location to another. Substantial savings to a paint manufacturer in materials and paint quality are achieved using the novel apparatus.

What is claimed is:

1. A process for measuring the light transmittance of a pigmented paint film which comprises 1. spraying pigmented paint on a strip of a heat resistant flexible transparent substrate to a sufficient thickness so that the paint film will render invisible to the unaided eye a contrasting background on one end of the strip and reducing the paint film thickness over the strip until the contrasting background is clearly visible and drying the paint;

2. measuring the light transmission of the paint film by passing the coated substrate prepared in step (1) and marking the coated substrate at the place where the light transmission value matches a predetermined standard light transmission value for the pigmented paint; and

3. measuring the thickness of the paint film at this marked place using a standard thickness gauge.

2. An improved process for pigmenting a paint to a level of pigmentation that provides a uniform hiding power at a given paint film thickness level which comprises l. spraying pigmented paint on a strip of a heat resistant flexible transparent substrate to a sufficient thickness so that the paint film will render invisible to the unaided eye a contrasting background on one end of the strip and reducing the paint film thickness over the strip until the contrasting background is clearly visible and drying the paint;

2. measuring the light transmission of the paint film by passing the coated substrate prepared in step (1) and marking the coated substrate at the place where the light transmission value matches a predetermined standard light transmission value of the paint;

3. measuring the thickness of the paint film at this marked place using a standard thickness gauge;

4. adding additional pigment to the paint if the paint film has a film thickness greater than the film thickness of the predetermined standard film thickness value for the paint or adding unpigmented paint vehicle to the paint if the paint film has a film thickness less than the film thickness of the predetermimed standard film thickness value for the paint and repeating steps (1) through (4) until the paint film has a light transmission value and paint film thickness of the predetermined standard. 

1. A process for measuring the light transmittance of a pigmented paint film which comprises
 1. spraying pigmented paint on a strip of a heat resistant flexible transparent substrate to a sufficient thickness so that the paint film will render invisible to the unaided eye a contrasting background on one end of the strip and reducing the paint film thickness over the strip until the contrasting background is clearly visible and drying the paint;
 2. measuring the light transmission of the paint film by passing the coated substrate prepared in step (1) and marking the coated substrate at the place where the light transmission value matches a predetermined standard light transmission value for the pigmented paint; and
 3. measuring the thickness of the paint film at this marked place using a standard thickness gauge.
 2. measuring the light transmission of the paint film by passing the coated substrate prepared in step (1) and marking the coated substrate at the place where the light transmission value matches a predetermined standard light transmission value for the pigmented paint; and
 2. An improved process for pigmenting a paint to a level of pigmentation that provides a uniform hiding power at a given paint film thickness level which comprises
 2. measuring the light transmission of the paint film by passing the coated substrate prepared in step (1) and marking the coated substrate at the place where the light transmission value matches a predetermined standard light transmission value of the paint;
 3. measuring the thickness of the paint film at this marked place using a standard thickness gauge;
 3. measuring the thickness of the paint film at this marked place using a standard thickness gauge.
 4. adding additional pigment to the paint if the paint film has a film thickness greater than the film thickness of the predetermined standard film thickness value for the paint or adding unpigmented paint vehicle to the paint if the paint film has a film thickness less than the film thickness of the predetermimed standard film thickness value for the paint and repeating steps (1) through (4) until the paint film has a light transmission value and paint film thickness of the predetermined standard. 